t health science reporter carolyn johnson looks at blue print on how we treat heart and print on how we treat heart and heart disease >> even through a microscope there is no miss taking the rift mick beating. living heart cell were created in a bay area lab and help researchers unlock the secret of how a heart becomes a heart. >> helps to have a blue print. to know what switches exist. how they are connected and what they turn on or shut off. >> so bruno and his team at san francisco glad stone institute set out to map the genetic switches locked inside the dna of of stem cell to see how a stem cell becomes a heart cell. >> with these the modification are doing is they are setting the right switches to turn gene on or off so that a heart cell in this case gains its heart identity. >>reporter: to begin researchers jeffrey alexander coax millions of stem cell taken from mice into becoming beating heart cell, process didn't in petrie dish and they mimic the environment in the woom. not always a pre-size sigh he says. >>y weekend sometimes wou hinge on whher i came in and saw the cells